1. Field of the Invention
This application relates to a socket for an integrated circuit component package and more specifically relates to an apparatus which can be used for socketing surface mount packages and to burn-in sockets which can be used with small packages such as a small outline integrated circuit package.
2. Description of the Prior Art
Dual in-line packages, or DIPs, are a standard means for packaging circuit elements such as integrated circuit chips. Each DIP consists of a main plastic body having two rows of leads extending downwardly therefrom for reception in plated-through holes or miniature spring sockets in a printed circuit board (PCB). Conventional DIP packages constitute the most common means for packaging integrated circuit chips. These small integrated circuit chips are bonded to a metal lead frame having a plurality of leads extending from opposite sides and stamped from the thin metal plate defining the lead frame. The chip and the portion of the lead frame surrounding the chip are encapsulated in a plastic body, leaving the stamped leads to extend outwardly from opposite sides of the plastic body. In a conventional DIP, these leads are then bent downwardly to form leads suitable for through-hole mounting in a printed circuit board. In order to reduce the possibility of damaging the leads and further to facilitate replacement of a conventional DIP, sockets suitable for receiving a conventional DIP can be mounted on the printed circuit board, thus permitting repeated insertion and withdrawal of the DIP from the socket. A low profile DIP socket having good contact properties and constant insertion force is disclosed in U.S. Pat. No. 4,060,296.
Some applications require that DIPs be temperature cycled or "burned-in" before use, to reduce the possibility of failure. For this purpose, sockets incorporating housings made from a temperature resistant material and including contacts offering low insertion force for engaging the DIP leads without imposing stress thereon during burn-in have been developed. One such socket is marketed by AMP incorporated as the DIPLOMATE HT (high temperature) socket.
In an effort to reduce the size of printed circuit board assemblies, new integrated circuit component packages such as the small outline integrated circuit have recently come into expanded use. The small outline integrated circuit package (SOIC) also has opposed rows of leads extending outwardly from the sides of an encapsulating plastic body. As the name would indicate, small outline integrated circuit components are significantly smaller than conventional DIPs. The centerline spacing between adjacent leads in an SOIC is significantly smaller than for a DIP. Small outline integrated circuit packages are also intended to be compatible with surface mount printed circuit board components, in which components are attached to pads on the surface of the printed circuit boards rather than having leads extending through holes in the printed circuit boards. Surface mounting technology is seen as offering significant advantages in increasing the density of components mounted on a printed circuit board. The leads on surface mount SOICs are bent downwardly from the sides of the SOIC plastic body, but the leads are also intended for soldering immediately in the vicinity of the lower surface of the plastic body. Thus with conventional SOICs, the leads are bent outwardly to form feet which are suitable for forming a lap joint on a surface mount pad. Other conventional surface mount joints might require different, though conventional, configurations of the leads extending from an SOIC.
Although SOICs are intended for direct, surface mount, attachment to a printed circuit board, the advantages of socketing integrated circuit packages, long perceived with conventional DIPs, would also apply to SOIC packages. For example, in evaluating the integrity of specific components by use of burn-in techniques, sockets from which the SOIC package could be readily removed would be necessary. Conventional burn-in socket configurations are unsuited for use with SOIC packages, in part because of the extremely close spacings of the SOIC leads and because of the fragility of the small leads in an SOIC package. Sockets for standard DIPs having contacts for receiving downwardly projecting leads are also quite unsuitable for engaging laterally projecting feet on conventional SOIC packages. One test socket used with SOICs is shown in U.S. Pat. No. 4,461,525.